Abstract During adult life, many organs rely on stem cells to maintain their integrity by replenishing lost cells during tissue homeostasis or in response to injury. Proliferation and differentiation of adult stem cells are under tight control in order to achieve the normal balance between removing dead cells and producing new cells. Disruption of the underlying regulatory mechanisms could result in excessive proliferation of stem cells/progenitor cells, leading to tumor formation. The Drosophila adult midgut has emerged as an attractive model to investigate how stem cell proliferation, self-renewal and differentiation are regulated, not only because the cell lineage in this tissue is relatively simple and well defined, but also because conserved genetic pathways and regulatory mechanisms are utilized in this system compared with mammalian systems. In addition, sophisticated genetic tools and the wealth of reagents available in the Drosophila community allow systematic identification and in-depth characterization of genes and pathways involved in intestine stem cell (ISC) biology. In recent years, we have demonstrated that tissue damage stimulates ISC proliferation and differentiation in Drosophila midgut. We have identified Insulin and Hippo (Hpo) signaling pathways as two critical pathways that regulate midgut homeostasis and regeneration. Because this system is relatively new, our understanding of ISC biology is still rudimentary. For example, the cellular and molecular basis of stem cell niche in the midgut has remained illusive. The goal of this research is to identify new genetic and molecular components that control Drosophila midgut homeostasis and regeneration with an emphasis on the regulatory mechanisms that control ISC self-renewal and proliferation. Toward this end, we have initiated a genetic screen and identified components in the Bone Morphogenic Protein (BMP) and Hedgehog (Hh) pathways as essential for midgut regeneration. We will investigate the function of BMP and Hh pathways in the regulation of ISC self-renewal and proliferation during normal tissue homeostasis and damage-induced regeneration. We will also identify other regulatory factors involved in midgut homeostasis and regeneration. The specific aims for this proposal are: 1) investigate the function and mechanism of BMP signaling in the regulation of ISC self-renewal; 2) investigate the regulation of BMP signaling and its interaction with other pathways in midgut regeneration; 3) investigate the role of Hh signaling in midgut homeostasis and regeneration; 4) identify and characterize new genes involved in midgut regeneration. The proposed study should provide better understanding of how extrinsic signals and intrinsic factors control stem cell proliferation, self-renewal and differentiation during adult tissue homeostasis and regeneration. The knowledge gained from this study will have important implications for cancer biology and regenerative medicine.